Vehicles may be required to have diagnostics to validate the integrity of fuel systems, such as a fuel evaporation collection system, for potential leaks. Natural vacuum techniques or engine vacuum techniques have been used to provide the vacuum level to run the diagnostic. Natural vacuum may be provided in a conventional vehicle from heat rejected from an operating internal combustion engine into the tank. With vehicles such as hybrids, the engine may never turn on during a drive cycle and natural vacuum may not be available.